In modern society, a light emitting diode (hereinafter, referred to as ‘LED’) has been used as a backlight unit (BLU) for a cellular phone, a backlight unit (BLU) for a LCD TV, and an optical treatment purpose, in an optical source for display, or has been actively entered into the market. Also, from now on an application field of the LED will gradually be widen even to a general illumination field such as an incandescent lamp or a fluorescent lamp so that the age of a semiconductor illumination has been expected to come in near future.
Generally, if the LED applies current to a single-layer chip or a multi-layer chip, electron-hole pairs excited in semiconductor layers and light emitting layers such as active layers provided between the semiconductor layers are combined to emit electric energy as light energy.
Therefore, a stacked structure of the LED where semiconductor layers doped with different types of impurities are sequentially stacked and the active layers are stacked therebetween has a form that electrode layers having types each corresponding to types of semiconductor layers are formed on regions of the semiconductor layers so as to connect to a power supply.
A sapphire substrate is mainly used as a substrate, and different types of semiconductor layers form a PN junction, wherein a light emitting layer may exist between a p-type semiconductor layer and an n-type semiconductor layer.
Meanwhile, since resistance of the p-type semiconductor layer is high, a transparent electrode layer having excellent conductivity may be stacked on an upper part of the p-type semiconductor and be used, in order to smooth current flow.
FIGS. 1A and 1B show a stacked structure of a light emitting diode according to one embodiment of the related art and a plan view viewing the light emitting diode from above.
Referring to FIG. 1A, an n-type semiconductor layer 101 made of material such as n-GaN, etc., a light emitting layer 102, and a p-type semiconductor layer 103 made of p-GaN, etc., are sequentially stacked on a substrate 100, wherein on a region of the n-type semiconductor layer 101 is provided an n-type electrode layer 105 having the same n-type, and on a region of the p-type semiconductor layer 103 is formed a transparent electrode layer 104 and on the transparent layer 104 is formed a p-type electrode layer 106 having the same p-type.
Generally, the n-type electrode layer 105 is applied with negative (−) power supply and the p-type electrode layer 106 is applied with positive (+) power supply to apply forward voltage to the light emitting diode, emitting light.
The plan view viewing the structure from above is the same as FIG. 1B, wherein the n-type electrode layer 105 and the p-type electrode layer 106 has a form that they are generally symmetrical or disposed in a row, the n-type electrode layer 105 and the p-type electrode layer 106 each being formed inside the same types of semiconductor layers.
FIG. 3A shows a circuit view of a conventional light emitting diode. A conventional diode serves as a resistor R1 when current flows, wherein when forward power supply is applied, the diode weakly acts as a resistor to allow current flow from a p-type semiconductor to an n-type semiconductor, and when reverse power supply is applied, the diode strongly acts as a resistor to allow current flow from the n-type semiconductor to the p-type semiconductor.
A structure of a light emitting diode and a form thereof may be a light emitting diode in a wire bonding structure where they are sequentially stacked according to a bonding manner to be provided in a circuit substrate, or be a light emitting diode in a flip-chip bonding structure (hereinafter, referred to as ‘flip-chip light emitting diode’) as shown in FIG. 6.
Referring to FIG. 6, the flip-chip light emitting diode is not different either from the conventional light emitting diode in view of the stacked structure, and the flip-chip light emitting diode merely turns upside down the stacked light emitting diode to bond it to an auxiliary substrate 608 using a solder ball 607 between the respective electrode layers 605 and 606 and the auxiliary substrate.
The light emitting diode itself of the conventional light emitting diode cannot but act as one resistor so that when the magnitude of current applied to the light emitting diode is large, it is sensitive to electrical impact and its ability to endure electrostatic discharge is low, causing a problem that reliability on operation properties is deteriorated.